The term "aliphatic isocyanate" refers to compounds in which the isocyanate group (--NCO) is attached to a carbon atom not in an aromatic ring, and hindered isocyanates are those in which the carbon atom to which the isocyanate group is attached is provided with at least one other inert substituent, generally a lower (C.sub.1 -C.sub.8) alkyl group. The preparation of polyurethanes from aliphatic isocyanates is well-known and the advantages derived therefrom are appreciated by those skilled in the art. Primary aliphatic isocyanates, for example, 1,6-hexamethylene diisocyanate, react significantly faster with compounds containing amino, carboxyl and hydroxyl groups than secondary or tertiary isocyanates. However, many isocyanates containing secondary and/or tertiary isocyanate groups are known and some of them provide highly useful polyurethane products. Unfortunately, they usually are exceedingly slow reacting and require catalysis, especially in reactions with hydroxyl-containing compounds.
Reaction injection molding, commonly referred to by the acronym RIM, is a relatively recent advance in polyurethane technology. The process requires fast polyurethane reactions, that is, on the order of seconds at temperatures in the range of about 25.degree.-40.degree. C. Commonly used polyurethane catalysts, such as lead naphthenate and dialkyl tin dicarboxylates, are not adequate to promote the reaction between hindered aliphatic isocyanates and hydroxyl-containing compounds under these conditions.
Jourquin and DuPrez, U.S. Pat. No. 4,150,206 (common disclosure to German OL No. 2,710,901) describe catalyst mixtures for making polyurethanes. Such mixtures, which comprise, typically, an amine compound of the partial formula ##STR1## and a lead compound, and, optionally, a tin compound, function to start the reaction quickly, open foamed cells at the end of the reaction, and produce polyurethanes with improved resistance to the development of color under artificial light.
Among the compounds exemplified in the '206 patent are those of the general formulae: ##STR2## wherein m is from 3 to 7 and n is from 2 to 4. Also exemplified is the compound 1,8-diazabicyclo(5.4.0)-undecene-7, a compound of the above formula, but one in which m is 3 and n is 5. This compound, and its salt with phenol, is shown in the '206 patent to be useful in catalyst systems only in combination with sodium acetate or sodium octoate, but not with tin compounds, alone, or even combined with lead compounds.